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Internet Engineering Task Force (IETF)                      M. KucherawyRequest for Comments: 6212                               Cloudmark, Inc.Category: Standards Track                                     April 2011ISSN: 2070-1721Authentication-Results Registration for Vouch by Reference ResultsAbstract   This memo updates the registry of properties in Authentication-   Results: message header fields to allow relaying of the results of a   Vouch By Reference query.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6212.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Kucherawy                    Standards Track                    [Page 1]

RFC 6212              Auth-Results VBR Registration           April 2011Table of Contents1. Introduction ....................................................22. Keywords ........................................................23. Discussion ......................................................24. Definition ......................................................35. IANA Considerations .............................................46. Security Considerations .........................................57. References ......................................................57.1. Normative References .......................................57.2. Informative References .....................................5Appendix A.  Authentication-Results Examples .......................6A.1.  VBR Results ................................................6Appendix B.  Acknowledgements ......................................71.  Introduction   [AUTHRES] defined a new header field for electronic mail messages   that presents the results of a message authentication effort in a   machine-readable format.  In the interim, a proposal for rudimentary   domain-level reputation assessment, called Vouch By Reference, [VBR]   was published and is now beginning to see popular use.   This memo thus registers an additional reporting property allowing a   VBR result to be relayed as an annotation in a message header.2.  Keywords   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [KEYWORDS].3.  Discussion   Vouch By Reference [VBR] introduced a mechanism by which a message   receiver can query a "vouching" service to determine whether or not a   trusted third party is willing to state that mail from a particular   source can be considered legitimate.  When this assessment is done at   an inbound border mail gateway, it would be useful to relay the   result of that assessment to internal mail entities such as filters   or user agents.   Reactions to the information contained in an Authentication-Results   header field that contains VBR (or any) results are not specified   here, as they are entirely a matter of local policy at the receiver.Kucherawy                    Standards Track                    [Page 2]

RFC 6212              Auth-Results VBR Registration           April 20114.  Definition   This memo adds to the "Email Authentication Methods" registry,   created by IANA upon publication of [AUTHRES], the following:   o  The method "vbr"; and   o  Associated with that method, the properties (reporting items)      "header.md" and "header.mv".   If "header.md" is present, its value MUST be the DNS domain name   about which a VBR query was made.  If "header.mv" is present, its   value MUST be the DNS domain name that was queried as the potential   voucher for the "header.md" domain.   If the VBR query was made based on the content of a "VBR-Info" header   field present on an incoming message, "header.md" is typically taken   from the "md" tag of the "VBR-Info" header field, and "header.mv" is   typically one of the values of the "mv" tag in the "VBR-Info" header   field on that message.  However, [VBR] permits a different mechanism   for selection of the subject domain and/or list of vouchers, ignoring   those present in any "VBR-Info" header field the message might have   included.  A server could even conduct a VBR query when no "VBR-Info"   field was present, based on locally configured policy options.  Where   such mechanisms are applied, the verifying server MAY generate an   Authentication-Results field to relay the results of the VBR query.   This memo also adds to the "Email Authentication Result Names"   registry the following result codes and definitions:   none:  No valid VBR-Info header was found in the message, or a domain      name to be queried could not be determined.   pass:  A VBR query was completed, and the vouching service queried      gave a positive response.   fail:  A VBR query was completed, and the vouching service queried      did not give a positive response, or the message contained      multiple VBR-Info header fields with different "mc" values      (see [VBR]).   temperror:  A VBR query was attempted but could not be completed due      to some error that is likely transient in nature, such as a      temporary DNS error.  A later attempt may produce a final result.Kucherawy                    Standards Track                    [Page 3]

RFC 6212              Auth-Results VBR Registration           April 2011   permerror:  A VBR query was attempted but could not be completed due      to some error that is likely not transient in nature, such as a      permanent DNS error.  A later attempt is unlikely to produce a      final result.5.  IANA Considerations   Per [IANA], the following items have been added to the "Email   Authentication Methods" registry:   +------------+----------+--------+----------------+-----------------+   |   Method   | Defined  | ptype  | property       | value           |   +------------+----------+--------+----------------+-----------------+   |    vbr     |RFC 6212 | header | md             | DNS domain name |   |            |          |        |                | used as the     |   |            |          |        |                | subject of a    |   |            |          |        |                | VBR query       |   +------------+----------+--------+----------------+-----------------+   |    vbr     |RFC 6212 | header | mv             | DNS domain name |   |            |          |        |                | of the entity   |   |            |          |        |                | acting as       |   |            |          |        |                | the voucher     |   +------------+----------+--------+----------------+-----------------+   Also, the following items have been added to the "Email   Authentication Result Names" registry:   +-----------+--------------+------------+---------+-----------------+   |   Code    | Existing/New | Defined In | Method  | Meaning         |   +-----------+--------------+------------+---------+-----------------+   | none      | existing     |RFC 5451  | vbr     |Section 4 of    |   |           |              |            | (added) |RFC 6212        |   +-----------+--------------+------------+---------+-----------------+   | pass      | existing     |RFC 5451  | vbr     |Section 4 of    |   |           |              |            | (added) |RFC 6212        |   +-----------+--------------+------------+---------+-----------------+   | fail      | existing     |RFC 5451  | vbr     |Section 4 of    |   |           |              |            | (added) |RFC 6212        |   +-----------+--------------+------------+---------+-----------------+   | temperror | existing     |RFC 5451  | vbr     |Section 4 of    |   |           |              |            | (added) |RFC 6212        |   +-----------+--------------+------------+---------+-----------------+   | permerror | existing     |RFC 5451  | vbr     |Section 4 of    |   |           |              |            | (added) |RFC 6212        |   +-----------+--------------+------------+---------+-----------------+Kucherawy                    Standards Track                    [Page 4]

RFC 6212              Auth-Results VBR Registration           April 20116.  Security Considerations   This memo creates a mechanism for relaying [VBR] results using the   structure already defined by [AUTHRES].  The Security Considerations   sections of those documents should be consulted.7.  References7.1.  Normative References   [AUTHRES]   Kucherawy, M., "Message Header Field for Indicating               Message Authentication Status",RFC 5451, April 2009.   [KEYWORDS]  Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [VBR]       Hoffman, P., Levine, J., and A. Hathcock, "Vouch By               Reference",RFC 5518, April 2009.7.2.  Informative References   [IANA]      Narten, T. and H. Alvestrand, "Guidelines for Writing an               IANA Considerations Section in RFCs",BCP 26,RFC 5226,               May 2008.Kucherawy                    Standards Track                    [Page 5]

RFC 6212              Auth-Results VBR Registration           April 2011Appendix A.  Authentication-Results Examples   This section presents an example of the use of this new header field   to indicate VBR results.A.1.  VBR Results   A message that triggered a VBR query, returning a result:        Authentication-Results: mail-router.example.net;              dkim=pass (good signature) header.d=newyork.example.com                    header.b=oINEO8hg;              vbr=pass (voucher.example.net)                    header.md=newyork.example.com                    header.mv=voucher.example.org        Received: from newyork.example.com                  (newyork.example.com [192.0.2.250])              by mail-router.example.net (8.11.6/8.11.6)                  for <recipient@example.net>                  with ESMTP id i7PK0sH7021929;              Fri, Feb 15 2002 17:19:22 -0800        DKIM-Signature: v=1; a=rsa-sha256; s=rashani;              d=newyork.example.com;              t=1188964191; c=relaxed/simple;              h=From:Date:To:VBR-Info:Message-Id:Subject;              bh=sEu28nfs9fuZGD/pSr7ANysbY3jtdaQ3Xv9xPQtS0m7=;              b=oINEO8hgn/gnunsg ... 9n9ODSNFSDij3=        From: sender@newyork.example.com        Date: Fri, Feb 15 2002 16:54:30 -0800        To: meetings@example.net        VBR-Info: md=newyork.example.com; mc=list;              mv=voucher.example.org        Message-Id: <12345.abc@newyork.example.com>        Subject: here's a sample   Example 1: Header Field Reporting Results from a VBR Query   Here we see an example of a message that was signed using DomainKeys   Identified Mail (DKIM) and that also included a VBR-Info header   field.  On receipt, it is found that the "md=" field in the latter   and the "d=" field in the former matched, and also that the DKIM   signature verified, so a VBR query was performed.  The vouching   service, voucher.example.org, indicated that the sender can be   trusted, so a "pass" result is included in the Authentication-Results   field affixed prior to delivery.Kucherawy                    Standards Track                    [Page 6]

RFC 6212              Auth-Results VBR Registration           April 2011Appendix B.  Acknowledgements   The author wishes to acknowledge the following for their review and   constructive criticism of this proposal: JD Falk, John Levine, and   Alessandro Vesely.Author's Address   Murray S. Kucherawy   Cloudmark, Inc.   128 King St., 2nd Floor   San Francisco, CA  94107   US   Phone: +1 415 946 3800   EMail: msk@cloudmark.comKucherawy                    Standards Track                    [Page 7]